The present invention relates to plastic pipe and pipe assemblies for use an geothermal heating and cooling systems. The invention has particular application to vertical geothermal systems, although it may also be used an horizontal systems. In addition the present invention has primary application to closed loop systems although the same pipe may also be used in open loop systems.
The earth has the ability to absorb and store heat energy. The geothermal heat pump system may thus extract heat from the earth through a liquid medium such as groundwater or an anti-freeze solution. The extracted heat may be used to heat a building. Conversely, heat may be extracted from a building and transferred to the earth. When changing from heating to cooling, or cooling to heating, the direction of fluid flow is reversed.
Geothermal heat pumps are increasingly being used to heat and cool both residential and commercial buildings. Such systems use this natural heat storage ability of the earth and/or the earth's groundwater to heat and cool. All heat pumps take heat from a first location and move that heat to a second location. In some cases, the temperature at the first location is lower than at the second location. Refrigerators and air conditioners are heat pumps which remove heat from colder interior spaces to warmer exterior spaces for cooling purposes. Heat pumps can move heat from a low temperature source to a high temperature space for heating. The movement of heat is accomplished with a vapor cycle that includes sequential evaporation, compression, condensation, and expansion. A refrigerant is used as the heat transfer medium and that medium circulates within the heat pump system.
There are two main types of loops: open and closed. A typical open-loop systems consumes water from a well. Closed loop systems use a continuous loop of plastic pipe buried in the earth. An anti-freeze solution circulates within the closed loop. The term anti-freeze is used herein to refer to the circulating fluid. Those skilled in the art will recognize that in climates in which no temperatures below the freezing temperature of water are known, the circulating fluid will typically be water. In those areas where temperatures fall below the freezing temperature of water the circulating fluid will be an anti-freeze solution such as an ethylene glycol solution. For convenience, the term antifreeze is used herein.
Horizontal loop systems typically have the loop disposed in a horizontal plane within a trench. Vertical loops in prior art systems have typically been used with substantially vertical shaft wells extending to the water table. A typical loop comprises first and second elongated straight legs that are each in fluid communication with a U-shaped section of pipe. Because such pipe has inherent limitations on the minimum radius of curvature that is possible without damaging the wall of the pipe, such structures inherently require a relatively large well bore to accommodate the loop. Because the cost of drilling the well rises geometrically with increases in well bore diameter this conventional prior art approach is not satisfactory. This prior art approach is also unsatisfactory because the part of the total surface area of two straight elongated tubes that is available for heat transfer is relatively limited.
Still another problem with the prior art structure that uses two elongated tubes joined at the lower extremity by an U-shaped pipe section is that this arrangement does not efficiently use the envelope of the well bore. It will be understood that, since wells are typically bored by a rotating tool, the well bore will ordinarily have a circular cross-section. Because the cross-section, taken in a horizontal plane, of the prior art construction will approximate the shape of the numeral "8" it follows that portions of the prior art structure will be relatively closely spaced to the wall of the well bore and other portions will be relatively widely spaced from the wall of the well bore.